Object measuring device and method for use in the device

ABSTRACT

Provided is an object measuring device capable of avoiding unnecessary scanning of an object that is unlikely to be an obstacle. By detecting a reflected light of a laser light emitted to an entire emission region, objects, other than a road surface, existing within the emission region are identified. When the objects other than the road surface are identified, a spread angle of the laser light, which is required for measuring the identified objects with a necessary accuracy, is determined. When the spread angle is determined, the laser light is emitted, at the determined spread angle, to the objects other than the road surface, and thereby the respective objects are measured.

TECHNICAL FIELD

The present invention relates to an object measuring device, and morespecifically relates to an object measuring device mounted in a mobilebody such as an automobile.

BACKGROUND ART

Conventionally, an object measuring device which uses a laser light formeasuring an object position and the like has been proposed. As anexample of such an object measuring device, an environment recognitionsystem (hereinafter referred to as a conventional art) disclosed inPatent Document 1 may be mentioned.

In the conventional art, while a measurement range is scanned by a laserlight, a distance image is generated based on a reflected lightreceived. In the conventional art, in order to shorten a time periodrequired for measuring, at a high resolution, an object existing withinthe measurement range, the measurement range is firstly scanned as astandard region, and a distance image is generated. The standard regionis scanned multiple times so that a plurality of distance images aregenerated. Then, in the conventional art, the distance images arecompared with each other, to detect differences among the respectivedistance images. Based on the detected differences, a position of amoving object is detected. When the position of the moving object isdetected, in the conventional art, a region, within the measurementrange, containing only the detected object is defined as a partialregion, and the partial region is scanned at a high resolution and at alower speed than for scanning the standard region. In the conventionalart, since only the region containing the detected object is scanned ata low speed, a time period required for scanning hardly increases evenin scanning an object at a high resolution.

-   Patent Document 1: Japanese Laid-open Patent Publication No.    2006-30147

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the conventional art described above raises the followingproblem. Namely, when using a method of comparing a plurality ofdistance images with each other to thereby detect a moving object asdescribed above, a region containing something, such as a line defininga section where an own vehicle is driving, which is unlikely to be anobstacle and thus need not to be detected is also detected as a partialregion. Thus, in the conventional art, the number of partial regionsexcessively increases, which may increase a time period required forperforming high-resolution scanning.

Therefore, an object of the present invention is to provide an objectmeasuring device capable of avoiding unnecessary measurement of anobject which need not to be measured.

Solution to the Problems

A first aspect of the present invention is directed to an objectmeasuring device mounted in a vehicle, including: a first emissionsection that emits, at a predetermined first spread angle, anelectromagnetic wave to a predetermined region; a reception section thatreceives, by receiving elements arranged in a grid pattern, a reflectedwave of the electromagnetic wave; a distance detection section thatdetects, for each of the receiving elements, a relative distance betweeneach receiving element and a reflection point of the reflected wave,based on a reception time period from emission of the electromagneticwave to reception of the reflected wave; a calculation section thatcalculates position information which indicates a position of thereflection point by using as a reference a position of mounting in thevehicle, based on at least the relative distance and an angle at whichthe reception section is mounted in the vehicle; a reference planecalculation section that calculates, as a reference plane, a planeparallel to a bottom surface of the vehicle, based on an orientation ofthe vehicle; an identification section that identifies, based on theposition information, adjacent reflection points, wherein a differencein height from the reference plane between the adjacent reflectionpoints is equal to or larger than a predetermined first threshold; and asecond emission section that emits, at a second spread angle which issmaller than the first spread angle, the electromagnetic wave to thereflection points, when the identification section identifies thereflection points.

In a second aspect of the present invention based on the first aspect,when the identification section identifies the reflection points, thesecond emission section emits the electromagnetic wave to the reflectionpoints, in order starting from the reflection point having the smallestrelative distance.

In a third aspect of the present invention based on the first aspect:the object measuring device further includes an object identificationsection that: groups the reflection points identified by theidentification section such that the adjacent reflection points whichare spaced from each other over a distance equal to or less than apredetermined second threshold are in one group; and identifies thereflection points in one group, as one object; and the second emissionsection emits the electromagnetic wave to the reflection points of theobject identified by the object identification section.

In a fourth aspect of the present invention based on the third aspect:the second emission section emits the electromagnetic wave to thereflection points, in order from the reflection point of the objectclosest to the object measuring device, among objects identified by theobject identification section; and the distance detection sectiondetects the relative distance for each object, in the order in which thesecond emission section has emitted the electromagnetic wave to theobjects.

In a fifth aspect of the present invention based on the fourth aspect,the distance detection section detects the relative distance for eachobject, based on the reception time period for receiving the reflectedwave having the highest intensity, among reflected waves reflected fromthe reflection points which have been grouped as the one object.

In a sixth aspect of the present invention based on the fifth aspect,after the distance detection section detects all the relative distancesfor the respective objects, the first emission section emits, at a thirdspread angle which is smaller than the first spread angle, theelectromagnetic wave to a next predetermined region immediatelyfollowing the region.

In a seventh aspect of the present invention based on any one of thefourth to sixth aspects, the object measuring device further includes aspeed detection section that detects, for each object, a relative speedbetween the object measuring device and the object, based on the mostrecent relative distance and the previously detected relative distancewhich are respectively detected by the distance detection section.

An eighth aspect of the present invention is directed to an objectmeasuring method which is performed in an object measuring devicemounted in a vehicle. The object measuring method includes: a firstemission step of emitting, at a predetermined first spread angle, anelectromagnetic wave to a predetermined region; a reception step ofreceiving, by receiving elements arranged in a grid pattern, a reflectedwave of the electromagnetic wave; a distance detection step ofdetecting, for each of the receiving elements, a relative distancebetween each receiving element and a reflection point of the reflectedwave, based on a reception time period from emission of theelectromagnetic wave to reception of the reflected wave; a calculationstep of calculating position information which indicates a position ofthe reflection point by using as a reference a position of mounting inthe vehicle, based on at least the relative distance and an angle atwhich the receiving element is mounted in the vehicle; a reference planecalculation step of calculating, as a reference plane, a plane parallelto a bottom surface of the vehicle, based on an orientation of thevehicle; an identification step of identifying, based on the positioninformation, adjacent reflection points, wherein a difference in heightfrom the reference plane between the adjacent reflection points is equalto or larger than a predetermined first threshold; and a second emissionstep of emitting, at a second spread angle which is smaller than thefirst spread angle, the electromagnetic wave to the reflection points,when the reflection points are identified in the identification step.

Effect of the Invention

According to the present invention, an object measuring device capableof avoiding unnecessary measurement of an object which need not to bemeasured can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing an example of a position at which an objectmeasuring device is mounted.

FIG. 1B is a diagram showing an example of the position at which theobject measuring device is mounted.

FIG. 2 is a block diagram showing a schematic configuration of theobject measuring device.

FIG. 3 is a diagram showing a more detailed configuration of an emissionsection.

FIG. 4A is a diagram showing an example of a relationship between adirection in which a diffusion plate is curved, and the width of a laserlight.

FIG. 4B is a diagram showing an example of the relationship between thedirection in which the diffusion plate is curved, and the width of thelaser light.

FIG. 4C is a diagram showing an example of the relationship between thedirection in which the diffusion plate is curved, and the width of thelaser light.

FIG. 5A is a diagram showing an example of a relationship between thewidth and a spread angle of the laser light.

FIG. 5B is a diagram showing an example of the relationship between thewidth and the spread angle of the laser light.

FIG. 6 is a diagram showing a direction in which a light-receivingposition on the diffusion plate, at which the laser light is received,is controlled.

FIG. 7A is a diagram showing an example of a relationship between thelight-receiving position on the diffusion plate, at which the laserlight is received, and a direction in which the laser light is emittedfrom the lens.

FIG. 7B is a diagram showing an example of the relationship between thelight-receiving position on the diffusion plate, at which the laserlight is received, and the direction in which the laser light is emittedfrom the lens.

FIG. 7C is a diagram showing an example of the relationship between thelight-receiving position on the diffusion plate, at which the laserlight is received, and the direction in which the laser light is emittedfrom the lens.

FIG. 8 is a functional block diagram showing functions of a controlcalculation section.

FIG. 9 is a diagram showing an example of an emission region.

FIG. 10 is a diagram showing a relative distance between alight-receiving element and a reflection point.

FIG. 11 is a diagram showing reflection points of an object and a roadsurface.

FIG. 12 is a diagram showing an example of a spread angle calculationtable.

FIG. 13 is a diagram showing an example of an object information table.

FIG. 14 is a flow chart illustrating a process performed by the controlcalculation section according to a first embodiment.

FIG. 15 is a diagram showing an example of a pattern image.

FIG. 16A is a diagram showing an example of an irradiation region on adistance image.

FIG. 16B is a diagram showing an example of an irradiation region on adistance image and an irradiation region on a pattern image.

FIG. 16C is a diagram showing an example of an irradiation region on adistance image and an irradiation region on a pattern image.

FIG. 17 is a diagram showing an example of another configuration of theemission section.

FIG. 18 is a diagram showing an example of another configuration of theemission section.

DESCRIPTION OF THE REFERENCE CHARACTERS

-   -   1 object measuring device    -   101 emission section    -   102 detection section    -   103 control calculation section    -   1031 distance detection section    -   1032 position calculation section    -   1033 obstacle identification section    -   1034 spread angle determination section    -   1035 correction section

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1A and FIG. 1B are diagrams illustrating one example of anapplication of an object measuring device 1 according to a firstembodiment of the present invention. The object measuring device 1 is,for example, attached around a license plate at the rear of an ownvehicle, such that a road surface Rm behind the own vehicle can bemeasured, as shown in FIG. 1A and FIG. 1B. The object measuring device 1emits a laser light Lk, which will be described later, to a part or thewhole of a detection range of a detection section 102, and receives, bythe detection section 102, a reflected light obtained by the emittedlaser light Lk being reflected from a reflection point Ht of an objectsuch as the road surface Rm or an obstacle Sb. The object measuringdevice 1 detects a relative distance St from the reflection point Ht ofthe object, based on a light-receiving time from the emission of thelaser light Lk to the reception of the reflected light by the detectionsection 102. Moreover, by using the relative distance St from thereflection point Ht, which has been detected, and on an angle (a pitchangle, a yaw angle, and a roll angle) at which the object measuringdevice 1 is attached to the own vehicle, the object measuring device 1calculates coordinates in a three-dimensional coordinate system based onan originating position Ki which is a position on a reference plane Kmvertically below the object measuring device 1, as shown in FIG. 1A andFIG. 1B. Here, for example, the reference plane Km is successivelycalculated, by a control calculation section 103, as a plane that isparallel to a bottom surface of the own vehicle in the aforementionedcoordinate system, based on an orientation of the own vehicle such as aninclination thereof, which is detected by the detection section (sensor)not shown. Hereinafter, the object measuring device 1 according to thepresent embodiment will be described in more detail.

FIG. 2 is a block diagram showing a schematic configuration of theobject measuring device 1 according to the first embodiment of thepresent invention. The object measuring device 1 includes an emissionsection 101, a detection section 102, and a control calculation section103.

FIG. 3 is a diagram showing a more detailed configuration of theemission section 101. The emission section 101 includes at least a lightsource 1011, a first reflecting plate 1012, a second reflecting plate1013, a diffusion plate 1014, and a lens 1015.

The light source 1011 is typically a laser light source which emits alaser light having a frequency in the infrared region, and emits thelaser light Lk to the first reflecting plate 1012.

The first reflecting plate 1012 is typically an MEMS (Micro ElectroMechanical System) mirror, and attached at an angle of 45 degrees withrespect to the optical axis of the laser light Lk such that the firstreflecting plate 1012 can orthogonally reflect the laser light Lkemitted from the light source 1011. Also, as shown in FIG. 3, the firstreflecting plate 1012 is attached so as to be movable along thedirection of the optical axis of the laser light Lk emitted from thelight source 1011. The first reflecting plate 1012 is moved by a drivingsection, which is not shown.

The second reflecting plate 1013 is typically an MEMS mirror, andattached in such a manner that the second reflecting plate 1013 canreflect the laser light Lk, which has been reflected by the firstreflecting plate 1012, toward the diffusion plate 1014. Also, as shownin FIG. 3, the second reflecting plate 1013 is attached so as to berotatable about the optical axis of the laser light Lk reflected by thefirst reflecting plate 1012. The second reflecting plate 1013 is rotatedby the driving section, which is not shown.

The diffusion plate 1014 is formed of a dielectric, such as apiezoelectric element capable of transmitting the laser light Lktherethrough, which is molded into a circular plate shape with apredetermined thickness. The diffusion plate 1014 has an edge thereoffixed. The diffusion plate 1014 is attached such that, in response tovoltage applied by the driving section not shown, a central portion of alight receiving surface of the diffusion plate 1014 can move along anaxis that passes through the center of the light receiving surface inthe direction perpendicular to the light receiving surface and therebythe diffusion plate 1014 can be curved. Instead of the piezoelectricelement, a liquid lens may be used for the diffusion plate 1014.

FIGS. 4A to 4C are diagrams each showing an example of the laser lightLk passing through the diffusion plate 1014. As shown in FIG. 4A, whenthe diffusion plate 1014 is not curved, that is, when, in the diffusionplate 1014, the light receiving surface and a transmitting surface forthe laser light Lk are parallel to each other, the laser light Lk passesthrough the diffusion plate 1014 without changing the width b thereof.When, as shown in FIG. 4B, the diffusion plate 1014 is curved so as toform a convex surface toward the lens 1015, the laser light Lk passingthrough the diffusion plate 1014 has the width b thereof decreased inaccordance with the degree of the curve. When, as shown in FIG. 4C, thediffusion plate 1014 is curved so as to form a convex surface toward thesecond reflecting plate 1013, the laser light Lk passing through thediffusion plate 1014 has the width b thereof increased in accordancewith the degree of the curve. As described above, by the diffusion plate1014 being curved in response to the voltage applied by the drivingsection not shown, the diffusion plate 1014 can transmit therethroughthe laser light Lk having been reflected by the second reflecting plate1013, while changing the width of the laser light Lk. In FIGS. 4A to 4C,illustration of a fixing unit for fixing the edge of the diffusion plate1014 is omitted for convenience of description.

The lens 1015 is typically a convex lens having a convex surfaceoriented in the direction in which the laser light Lk is emitted. Asshown in FIGS. 5A and 5B, the lens 1015 refracts the laser light Lkhaving passed through the diffusion plate 1014, and radially emits thelaser light Lk from an emitting surface. Each of FIGS. 5A and 5B is adiagram illustrating a relationship between the width b of the laserlight Lk having passed through the diffusion plate 1014 and the spreadangle Hk of the laser light Lk emitted from the emitting surface of thelens 1015.

In examples shown in FIGS. 5A and 5B, as apparent from the comparisonbetween FIGS. 5A and 5B, the width b of the laser light Lk shown in FIG.5B is larger than the width b of the laser light Lk shown in FIG. 5A. Asapparent from the comparison between FIGS. 5A and 5B, when the laserlight Lk having the larger width b passes through the lens 1015, theresulting spread angle Hk is larger. That is, the emission section 101according to the present embodiment can control the spread angle Hk ofthe laser light Lk emitted from the emitting surface of the lens 1015,by curving the diffusion plate 1014 and thereby changing the width b ofthe laser light Lk.

FIG. 6 is a diagram illustrating an example of a relationship among adirection in which the first reflecting plate 1012 is moved, a directionin which the second reflecting plate 1013 is rotated, and alight-receiving position, on the diffusion plate 1014, at which thelaser light Lk is received. FIG. 6 shows an example of the diffusionplate 1014 when viewed from the second reflecting plate 1013 toward thelens 1015. As shown in FIG. 6, the emission section 101 causes the firstreflecting plate 1012 to move, by the driving section not shown, alongthe direction of the optical axis of the laser light Lk which is emittedfrom the light source 1011, and thereby can control the horizontalposition of the light-receiving position, on the light receiving surfaceof the diffusion plate 1014, at which the laser light Lk is received.Moreover, as shown in FIG. 6, the emission section 101 causes the secondreflecting plate 1013 to rotate about the optical axis of the laserlight Lk having been reflected by the first reflecting plate 1012, bythe driving section not shown, and thereby can control the verticalposition of the light-receiving position, on the light receiving surfaceof the diffusion plate 1014, at which the laser light Lk is received.

FIGS. 7A to 7C are diagrams each showing an example of a relationshipbetween the horizontal position of the light-receiving position on thediffusion plate 1014 at which the laser light Lk is received, and theemission direction in which the laser light Lk is emitted from the lens1015. As shown in FIG. 7A, when the horizontal position of thelight-receiving position on the diffusion plate 1014 at which the laserlight Lk is received is shifted leftward from the center of the lightreceiving surface for example, a horizontal angle Sh of the emissiondirection in which the laser light Lk is emitted from the lens 1015changes in accordance with the amount of the shift so as to orient theemission direction to the left. As shown in FIG. 7B, when thelight-receiving position on the diffusion plate 1014 at which the laserlight Lk is received is made coincident with the center of the lightreceiving surface of the lens 1015, the emission direction in which thelaser light Lk is emitted from the lens 1015 is oriented to the front ofthe emitting surface. As shown in FIG. 7C, when the horizontal positionof the light-receiving position on the diffusion plate 1014 at which thelaser light Lk is received is shifted rightward from the center of thelight receiving surface, a horizontal angle Sh of the emission directionin which the laser light Lk is emitted from the lens 1015 changes inaccordance with the amount of the shift so as to orient the emissiondirection to the right. That is, in the emission section 101 accordingto the present embodiment, the first reflecting plate 1012 is movedalong the optical axis direction of the laser light Lk emitted from thelight source 1011, to thereby shift the horizontal position of thelight-receiving position, on the light receiving surface of thediffusion plate 1014, at which the laser light Lk having been reflectedby the second reflecting plate 1013 is received. In this manner, thehorizontal angle Sh of the emission direction in which the laser lightLk is emitted from the emitting surface of the lens 1015 can becontrolled. Here, the horizontal angle Sh is an angle which is formed,in the horizontal direction, between the optical axis of the laser lightLk emitted from the emitting surface of the lens 1015 and the axis thatpasses through the center of the emitting surface of the lens 1015 inthe direction perpendicular to the emitting surface of the lens 1015.

In the same manner, when the vertical position of the light-receivingposition on the diffusion plate 1014 at which the laser light Lk isreceived is shifted upward from the center of the light receivingsurface, a vertical angle Vk of the emission direction in which thelaser light Lk is emitted from the lens 1015 changes in accordance withthe amount of the shift so as to orient the emission direction upward.When the light-receiving position on the diffusion plate 1014 at whichthe laser light Lk is received is made coincident with the center of thelight receiving surface of the lens 1015, the emission direction inwhich the laser light Lk is emitted from the lens 1015 is oriented tothe front of the emitting surface. When the vertical position of thelight-receiving position on the diffusion plate 1014 at which the laserlight Lk is received is shifted downward from the center of the lightreceiving surface, the vertical angle Vk of the emission direction inwhich the laser light Lk is emitted from the lens 1015 changes inaccordance with the amount of the shift so as to orient the emissiondirection downward. That is, in the emission section 101 according tothe present embodiment, the second reflecting plate 1013 is rotatedabout the optical axis of the laser light Lk emitted from the lightsource 1011, to thereby control the vertical angle Vk of the emissiondirection in which the laser light Lk is emitted from the emittingsurface of the lens 1015. Here, the vertical angle Vk is an angle whichis formed, in the vertical direction, between the optical axis of thelaser light Lk emitted from the emitting surface of the lens 1015 andthe axis that passes through the center of the emitting surface of thelens 1015 in the direction perpendicular to the emitting surface of thelens 1015.

As described above with reference to FIGS. 4A to 7C, the emissionsection 101 according to the present embodiment drives the firstreflecting plate 1012, the second reflecting plate 1013, and thediffusion plate 1014 by the driving section which is not shown, andthereby the laser light Lk is emitted so as to have the spread angle Hkand the emission direction (the horizontal angle Sh and the verticalangle Vk) in accordance with an instruction indicating an emissionregion, which is provided by a distance detection section 1031 as willbe described later.

The detection section 102 is typically a solid-state imaging device inwhich light-receiving elements such as CCD (Charge Coupled Device)elements are arranged in a grid pattern on a flat substrate, and areflected light, which is obtained by the laser light Lk emitted fromthe emission section 101 being reflected from the reflection point Ht,is received by each of the light-receiving elements via a lens. When aninstruction to start a charge storage for a predetermined first timeperiod is provided by the distance detection section 1031 as will bedescribed later, the detection section 102 starts to store, through thefirst time period, a charge corresponding to the amount of lightreceived by each of the light-receiving elements. In the first timeperiod, since the laser light Lk is not emitted from the emissionsection 101, a charge stored by each of the light-receiving elements ofthe detection section 102 is a charge corresponding to the amount ofonly an ambient stray light (such as sunlight) received. When the firsttime period elapses, the detection section 102 stops the charge storagewhich has been performed by each of the light-receiving elements.

When the first time period elapses, the detection section 102 accordingto the present embodiment immediately starts a charge storage again byeach of the light-receiving elements, for a predetermined second timeperiod. Almost at the same time, an instruction to emit the laser lightLk is provided by the distance detection section 1031 to the emissionsection 101, as will be described later. Therefore, a charge stored byeach of the light-receiving elements through the second time period is acharge corresponding to the amount of an ambient stray light and theaforesaid reflected light which are received. When the second timeperiod elapses, the detection section 102 stops the charge storage whichhas been performed by each of the light-receiving elements.

When the detection section 102 stops the charge storage for the secondtime period, the detection section 102 detects, for each of thelight-receiving elements, a differential charge which is obtained bysubtracting the charge stored through the second time period from thecharge stored through the first time period. The differential chargewhich is obtained by subtracting the charge stored through the secondtime period from the charge stored through the first time period is acharge corresponding to the amount of only the reflected light received,which is obtained by subtracting the stored charge corresponding to theamount of only the ambient stray light received, from the stored chargecorresponding to the amount of the ambient stray light and the reflectedlight which are received. In a time period obtained by subtracting theaforesaid first and second time periods from a predetermined third timeperiod, the detection section 102 detects, for each of thelight-receiving elements, the charge corresponding to the amount of onlythe reflected light received. When the third time period elapses afterthe distance detection section 1031 has provided, to the detectionsection 102, the instruction to start a charge storage for the firsttime period, the distance detection section 1031 detects the charge ineach of the light-receiving elements, which has been detected by thedetection section 102. When the third time period elapses and the chargein each of the light-receiving elements is detected by the distancedetection section 1031, the detection section 102 resets the chargedetected in each of the light-receiving elements.

The control calculation section 103 is typically an arithmetic circuitmainly including an integrated circuit such as a CPU (Central ProcessingUnit). The control calculation section 103 functions at least as thedistance detection section 1031, a position calculation section 1032, anobstacle identification section 1033, and a spread angle determinationsection 1034, as shown in FIG. 8. To be more specific, the controlcalculation section 103 causes the CPU to execute a program stored in astorage section, not shown, such as a ROM (Read Only Memory), to therebycause the CPU to function as the distance detection section 1031, theposition calculation section 1032, the obstacle identification section1033, and the spread angle determination section 1034.

FIG. 9 is a diagram showing an example of an emission region which ispredefined in the storage section, not shown, of the control calculationsection 103. FIG. 9 shows, as an example, three emission regions Hr1 toHr3 which are predefined in the storage section, not shown, of thecontrol calculation section 103. The emission region Hr1 to the emissionregion Hr3 decrease the spread angle Hk in order, respectively. Thesmaller the spread angle Hk is, the greater the distance over which thelaser light Lk is emitted becomes.

The control calculation section 103 according to the present embodimentcontrols the emission section 101 and the detection section 102,respectively, so as to perform a measurement by emitting the laser lightLk to the three emission regions shown in FIG. 9, in order starting fromthe emission region Hr1 having the smallest emission distance to theemission region Hr3 having the greatest emission distance. Here, thespread angle Hk (hereinafter referred to as an emission region angleHrk) of the emission region shown in FIG. 9 is decreased such that theemission region angle Hrk 1 of the emission region Hr1 to the emissionregion angle Hrk3 of the emission region Hr3 decrease in order,respectively. By decreasing the emission region angle Hrk to therebynarrow the emission region, a light energy density per emission regionincreases. Even if laser lights Lk have the same intensity, the laserlight Lk having a higher light energy density reaches further. That is,the control calculation section 3 according to the present embodimentcauses the emission section 101 to narrow the emission region angle Hrkwithout increasing the intensity of the laser light Lk, and thereby canincrease the light energy density per emission region and cause thelaser light Lk to reach further.

When measuring the emission region Hr1, the control calculation section103 firstly performs an object identification process in which: anobject existing in the emission region Hr1 is identified; and an objectinformation table indicating information of the identified object isgenerated and stored in the storage section, not shown. In thefollowing, the object identification process by the control calculationsection 103 will be described. In the following description, as anexample of the object identification process, an object identificationprocess for identifying an object existing in the emission region Hr1will be described in detail.

When performing the object identification process for the emissionregion Hr1, the control calculation section 103 firstly causes thedistance detection section 1031 to provide the detection section 102with an instruction to start a charge storage for the first time period,as described above. Then, when the first time period elapses after theinstruction to start a charge storage for the first time period has beenprovided to the detection section 102, and subsequently the detectionsection 102 starts a charge storage for the second time period asdescribed above, the control calculation section 103 causes the distancedetection section 1031 to provide the emission section 101 with aninstruction to emit a laser light Lk to the emission region Hr1.

When the instruction indicating the emission region is provided by thedistance detection section 1031, the emission section 101 drives thefirst reflecting plate 1012, the second reflecting plate 1013, and thediffusion plate 1014 by the driving section which is not shown, asdescribed above, so as to emit a laser light Lk from the light source1011 to the entire emission region (here, the emission region Hr1)having been indicated by the instruction, for a predetermined emissionperiod.

When the aforesaid third time period elapses after the instruction tostart a charge storage for the first time period has been provided, thecontrol calculation section 103 causes the distance detection section1031 to detect a charge which has been detected, for eachlight-receiving element, by the detection section 102 as describedabove. When the control calculation section 103 detects the charge whichhas been detected for each light-receiving element by the detectionsection 102, the control calculation section 103 calculates, for eachlight-receiving element, a relative distance St between eachlight-receiving element storing the charge and the reflection point Htfrom which the reflected light to be received by the light-receivingelement has been reflected, based on the detected charge.

More specifically, the ratio between the most recent charge of alight-receiving element, which is detected by the distance detectionsection 1031 of the control calculation section 103 when the third timeperiod elapses, and the charge of the same light-receiving elementhaving been detected for the immediately preceding time, has a certainrelationship with the relative distance St between the light-receivingelement and the reflection point Ht of the object from which thereflected light to be received by the light-receiving element has beenreflected. Therefore, based on the ratio between the most recent charge,which is detected for each light-receiving element of the detectionsection 102 by the distance detection section 1031, and the chargehaving been detected for the immediately preceding time, the controlcalculation section 103 calculates the relative distance St between eachlight-receiving element and the reflection point Ht so as to associatethe relative distance St with each light-receiving element. When thecontrol calculation section 103 calculates the relative distance St foreach light-receiving element, the distance detection section 1031 iscaused to generate relative distance information Sj which indicates alight-receiving element and a relative distance St in association witheach other.

When the distance detection section 1031 of the control calculationsection 103 generates the relative distance information Sj, the distancedetection section 1031 of the control calculation section 103 convertsthe relative distance St associated with a light-receiving element, intoa brightness value indicating a brightness exhibited when the relativedistance St is displayed on a display screen in which pixelscorresponding to the respective light-receiving elements are arranged ina grid pattern. When the distance detection section 1031 converts therelative distance St associated with a light-receiving element, into abrightness value of a pixel corresponding to the light-receivingelement, the distance detection section 1031 of the control calculationsection 103 generates distance image information Kj which indicates, asa distance image, an image formed of the pixels that have brightnessvalues obtained as a result of the conversion.

When the distance detection section 1031 of the control calculationsection 103 generates the relative distance information Sj, the positioncalculation section 1032 is caused to acquire the generated relativedistance information Sj. When the position calculation section 1032acquires the relative distance information Sj, the control calculationsection 103 calculates a position of a reflection point Ht in theabove-described coordinate system, based on the position of alight-receiving element in the detection section 102, which is indicatedby the relative distance information Sj, and on a relative distance Stwhich is indicated in association with the light-receiving element bythe relative distance information Sj. The position calculation section1032 is caused to generate reflection point information Hj whichindicates the position of the reflection point Ht having beencalculated, in association with each light-receiving element indicatedby the relative distance information Sj.

FIG. 10 is a diagram illustrating a method for calculating, by theposition calculation section 1032 of the control calculation section103, a position of a reflection point Ht in the above-describedcoordinate system, based on the position of a light-receiving element inthe detection section 102, and on the relative distance St which isindicated in association with the light-receiving element by therelative distance information Sj. FIG. 10 is a plan view showing apositional relationship between the light-receiving elements arranged ina grid pattern on a flat substrate and a reflection point Ht from whicha light is reflected to one of the light-receiving elements, when viewedfrom the above in the vertical direction. As apparent from FIG. 10, whenperpendicular lines are drawn to a line passing through the center ofthe substrate perpendicularly to the substrate, from a light-receivingelement and the reflection point Ht from which a light is reflected tothe light-receiving element, respectively; two similar right-angledtriangles can be drawn by using a straight line passing through thelight-receiving element and the reflection point Ht from which the lightis reflected to the light-receiving element. The length of each side ofa right-angled triangle, which includes the light-receiving element andthe perpendicular line extending from the light-receiving element to theline that passes through the center of the substrate perpendicularly tothe substrate, is known, because the arrangement position of thelight-receiving element is known. Accordingly, the position calculationsection 1032 can calculate the x-coordinate and the y-coordinate of thereflection point Ht from which the light is reflected to thelight-receiving element, based on the ratio between the length St1 ofthe hypotenuse of the right-angled triangle including the arrangementposition of the light-receiving element, and the relative distance St2between the light-receiving element and the reflection point Ht, asviewed from the above in the vertical direction as shown in FIG. 10.

Similarly, when a positional relationship between the light-receivingelements arranged in a grid pattern on the flat substrate and areflection point Ht from which a light is reflected to one of thelight-receiving elements is viewed edge-on in the horizontal direction,two right-angled triangles can be drawn. The length of each side of aright-angled triangle, which includes a light-receiving element and aperpendicular line extending from the light-receiving element to theline passing through the center of the substrate perpendicularly to thesubstrate, is known, because the arrangement position of thelight-receiving element is known. Accordingly, the position calculationsection 1032 can calculate the z-coordinate of the reflection point Htfrom which the light is reflected to the light-receiving element, basedon the ratio between the length of the hypotenuse of the right-angledtriangle including the arrangement position of the light-receivingelement and the relative distance between the light-receiving elementand the reflection point Ht, as viewed edge-on in the horizontaldirection.

The control calculation section 103 converts positions represented bythe x-coordinate, the y-coordinate, and the z-coordinate, which havebeen respectively calculated by the position calculation section 1032,into positions, respectively, in the above-described coordinate system,based on the predetermined angle at which the object measuring device 1is attached to the own vehicle. When the position calculation section1032 of the control calculation section 103 converts the position of areflection point Ht for every light-receiving element indicated by therelative distance information Sj, the position calculation section 1032of the control calculation section 103 generates reflection pointinformation Hj which indicates, in association with everylight-receiving element, the position of the reflection point Ht whichis obtained as a result of the conversion.

When the position calculation section 1032 of the control calculationsection 103 generates the reflection point information Hj, the obstacleidentification section 1033 of the control calculation section 103acquires the generated reflection point information Hj. When theobstacle identification section 1033 acquires the reflection pointinformation Hj, the obstacle identification section 1033 of the controlcalculation section 103 identifies, as an object reflection point Th,the reflection point Ht of a vehicle, a pedestrian, an obstacle, or thelike, which exists on the road surface Rm, among the reflection pointsHt indicated by the acquired reflection point information Hj.

FIG. 11 is a diagram showing an example of the object reflection pointTh which is identified by the obstacle identification section 1033 ofthe control calculation section 103 based on the position of thereflection point Ht indicated by the reflection point information Hj.FIG. 11 shows, as an example, four reflection points Ht1 to Ht4indicated by the reflection point information Hj. In FIG. 11: theheights of the reflection points Ht1 and Ht2 from the above-describedreference plane Km are identical to each other; an inclination(difference) formed between the heights of the reflection points Ht2 andHt3 from the above-described reference plane Km is larger than apredetermined first threshold; and the heights of the reflection pointsHt3 and Ht4 from the above-described reference plane Km are identical toeach other.

As shown in FIG. 11, based on the positions of the reflection points Htindicated by the reflection point information Hj, the obstacleidentification section 1033 of the control calculation section 103identifies, as a reflection point Ht on the road surface Rm, such areflection point Ht (in the example shown in FIG. 11, the reflectionpoints Ht1 and Ht4) that the height thereof and the height of anadjacent reflection point Ht from the reference plane Km form aninclination equal to or less than the first threshold. On the otherhand, based on the positions of the reflection points Ht indicated bythe reflection point information Hj, the obstacle identification section1033 of the control calculation section 103 identifies, as a face of anobject other than the road surface Rm, such a reflection point Ht (thereflection points Ht2 and Ht3) that the height thereof and the height ofan adjacent reflection point Ht from the reference plane Km form aninclination larger than the first threshold. Here, in the presentembodiment, a reflection point Ht (in the example shown in FIG. 11, thereflection points Ht2 and Ht3) existing at a boundary between the roadsurface Rm and an object is identified as a reflection point Ht of theobject. That is, in the example shown in FIG. 11, the reflection pointsHt1 and Ht4 are identified as the reflection points Ht on the roadsurface Rm, and the reflection points Ht2 and Ht3 are identified as thereflection points Ht of the object.

The obstacle identification section 1033 of the control calculationsection 103 identifies the identified reflection point Ht of the object,as the object reflection point Th. Since the obstacle identificationsection 1033 of the control calculation section 103 identifies theobject reflection point Th; among the reflection points Ht indicated bythe reflection point information Hj, a reflection point Ht of an objectother than the road surface Rm, such as a vehicle, a pedestrian, and anobstacle, can be identified as the object reflection point Th, which canbe distinguished from the reflection point Ht of the road surface Rm.Here, the control calculation section 103 may identify, as the objectreflection point Th, such a reflection point Ht that the height thereofand the height of an adjacent reflection point Ht from the referenceplane form an inclination equal to or larger than a predeterminedthreshold.

When identifying the object reflection point Th, the obstacleidentification section 1033 of the control calculation section 103recognizes, based on the positions of the object reflection points Thindicated by the reflection point information Hj, object reflectionpoints Th located adjacent to each other over a distance equal to orless than a predetermined second threshold, as object reflection pointsTh for one object, and classifies the adjacent object reflection pointsTh into the same group. When all the object reflection points Th areclassified into groups, the control calculation section 103 identifies,among the object reflection points Th for one object which have beenrecognized by the obstacle identification section 1033, the objectreflection point Th closest to the object measuring device 1, based onthe positions indicated by the reflection point information Hj. Then,the control calculation section 103 recognizes the position of theobject reflection point Th thus identified, as the position of theobject. When the obstacle identification section 1033 of the controlcalculation section 103 recognizes positions of all objects, the controlcalculation section 103 generates object position information Tj whichindicates each recognized object, object reflection points Th for theobject, and a position of the object, in association with one another.Here, the object reflection point Th to be recognized as the position ofthe object does not always have to be the object reflection point Thclosest to the object measuring device 1 among the object reflectionpoints Th for the one object.

When the distance detection section 1031 of the control calculationsection 103 generates the distance image information Kj, the obstacleidentification section 1033 of the control calculation section 103acquires the generated distance image information Kj. Then, when theobstacle identification section 1033 of the control calculation section103 generates the object position information Tj, the controlcalculation section 103 identifies, as a pixel group representing oneobject, all of pixels on the distance image which correspond tolight-receiving elements, respectively, having received lights reflectedfrom object reflection points Th which are associated with the oneobject by the object position information Tj generated. When the pixelgroup representing one object is identified, the obstacle identificationsection 1033 of the control calculation section 103 detects the maximumwidth and the maximum height of the identified pixel group on thedistance image, as the size of the object. When the sizes of all theobjects indicated by the object position information Tj are detected,the obstacle identification section 1033 of the control calculationsection 103 generates size information Oj which indicates all theobjects and the sizes of the respective objects in association with eachother.

When the position calculation section 1032 of the control calculationsection 103 generates the reflection point information Hj, the spreadangle determination section 1034 of the control calculation section 103acquires the reflection point information Hj generated. When theposition calculation section 1032 of the control calculation section 103generates the distance image information Kj, the spread angledetermination section 1034 of the control calculation section 103acquires the distance image information Kj generated. When the obstacleidentification section 1033 of the control calculation section 103generates the object position information Tj and the size informationOj, the spread angle determination section 1034 of the controlcalculation section 103 acquires the object position information Tj andthe size information Oj generated.

When the spread angle determination section 1034 acquires the distanceimage information Kj and the object position information Tj, the controlcalculation section 103 identifies, based on the distance imageinformation Kj, a brightness value of a pixel that corresponds to alight-receiving element having received a light reflected from theposition of one object, which is indicated by the object positioninformation Tj, as a brightness value of the one object. When thebrightness value of the one object is identified, the spread angledetermination section 1034 of the control calculation section 103calculates an S/N ratio in the corresponding pixel as an S/N ratio ofthe object, based on the identified brightness value. Here, the S/Nratio in the present invention is a ratio between the intensity of thereflected light of the laser light Lk emitted from the emission section101 and a noise (such as a dark current and a noise occurring intransferring a charge) of a circuit included in the detection section102. The spread angle determination section 1034 of the controlcalculation section 103 calculates the S/N ratio in the correspondingpixel, based on the brightness value of the one object, a certainrelationship at the time of converting the relative distance St into abrightness value of the distance image, the above-described certainrelationship between the relative distance St and the charge, apredicted noise of the circuit, and the like.

When S/N ratios of all the objects indicated by the object positioninformation Tj are calculated, the spread angle determination section1034 of the control calculation section 103 generates signal intensityinformation Sk which indicates all the objects and the calculated S/Nratios of the respective objects, in association with each other.

When the spread angle determination section 1034 generates the signalintensity information Sk, the spread angle determination section 1034 ofthe control calculation section 103 calculates a required spread angleHh, based on a required S/N ratio, which is in advance stored in thestorage section, not shown, so as to correspond to each of the emissionregions described above, and on an S/N ratio of each object indicated bythe signal intensity information Sk. Here, as described above, the S/Nratio in the present invention is a ratio between the intensity of thereflected light of the laser light Lk emitted from the emission section101 and a noise (such as a dark current and a noise occurring intransferring a charge) of a circuit included in the detection section102. The higher the intensity of the reflected light is, the higher thecharge stored in the light-receiving element becomes, which improves(raises) the S/N ratio. In addition, the relative distance St iscalculated based on the ratio between the most recent charge detected bythe distance detection section 1031 and the charge having been detectedfor the immediately preceding time as described above. Therefore, as theS/N ratio is higher and the charge detected by the distance detectionsection 1031 is higher, the relative distance St is calculated with anincreased accuracy.

The above-mentioned required S/N ratio is a predetermined S/N ratiowhich is required for calculating the relative distance St with anaccuracy necessary for each emission region. Based on the S/N ratio ofan object, which is indicated by the signal intensity information Sk,and the required S/N ratio, the spread angle determination section 1034determines the required spread angle Hh for measurement, with anecessary accuracy, of the relative distance St of the object.

FIG. 12 is a diagram showing an example of a spread angle calculationtable which is stored in a storage section, not shown, and used when thespread angle determination section 1034 of the control calculationsection 103 determines the required spread angle Hh. With reference toFIG. 12, a method for determining the required spread angle Hh by thespread angle determination section 1034 of the control calculationsection 103 will be described. Firstly, the control calculation section103 identifies, among the plurality of emission regions described above,the emission region obtained at the time when the spread angledetermination section 1034 generates the signal intensity informationSk. When the emission region is identified (here, the emission regionHr1 is identified), the spread angle determination section 1034 of thecontrol calculation section 103 identifies, from the spread anglecalculation table shown in FIG. 12, a relative S/N ratio correspondingto the spread angle that is closest to the emission region angle Hrk ofthe identified emission region. When the relative S/N ratio isidentified, the spread angle determination section 1034 of the controlcalculation section 103 calculates, as a difference S/N ratio, a ratiobetween the S/N ratio of the object indicated by the signal intensityinformation Sk and the required S/N ratio which is predetermined so asto correspond to the identified emission region. The spread angledetermination section 1034 of the control calculation section 103identifies, from the spread angle calculation table shown in FIG. 12,the spread angle Hk corresponding to the relative S/N ratio that isclosest to an S/N ratio obtained by multiplying the identified relativeS/N ratio by the difference S/N ratio.

When the spread angle determination section 1034 of the controlcalculation section 103 identifies the spread angle Hk, the spread angledetermination section 1034 determines whether or not the identifiedspread angle Hk is equal to or greater than the emission region angle(here, the emission region angle Hrk 1 of the emission region Hr1). Whenthe spread angle determination section 1034 determines that theidentified spread angle Hk is not equal to or greater than the emissionregion angle, the control calculation section 103 determines theidentified spread angle Hk as a required spread angle Hh for the objectindicated by the signal intensity information Sk. On the other hand,when the identified spread angle Hk is equal to or greater than theemission region angle, the spread angle determination section 1034determines, as the required spread angle Hh, an angle obtained bymultiplying the emission region angle by a predetermined constant lessthan 1.

In the spread angle calculation table shown in FIG. 12, the spread angleHk is set so as to decrease as the relative S/N ratio increases. Whenthe spread angle determination section 1034 of the control calculationsection 103 determines that the identified spread angle Hk is equal toor greater than the emission region angle, an angle that is obtained bymultiplying the emission region angle by the predetermined constant lessthan 1 is determined as the required spread angle Hh. Accordingly, therequired spread angle Hh determined by the spread angle determinationsection 1034 is an angle smaller than the emission region angle (in theexample described above, the emission region angles Hrk1 to Hrk3) whichis predetermined for each emission region (in the example describedabove, the emission regions Hr1 to Hr3).

By calculating the required spread angle Hh in the above-describedmanner, the spread angle determination section 1034 of the controlcalculation section 103 can determine, as the required spread angle Hh,an spread angle for measuring, with a necessary accuracy, a relativedistance St to each reflection point Ht of the object, based on the S/Nratio of an object indicated by the signal intensity information Sk.When required spread angles Hh for all the objects indicated by thesignal intensity information Sk are determined, the spread angledetermination section 1034 of the control calculation section 103generates required spread angle information Hj which indicates thedetermined required spread angle Hh in association with each object.

The table shown in FIG. 12 is illustrative, and the table may have anyvalue as long as the spread angle Hk is set so as to decrease as therelative S/N ratio increases. In addition, the table shown in FIG. 12 isillustrative, and the relative S/N ratio may be any value as long as thetable can set the required spread angle Hh that is optimal.

When the object position information Tj, the size information Oj, thesignal intensity information Sk, and the required spread angleinformation Hj are generated, the distance detection section 1031 of thecontrol calculation section 103 acquires the respective informationgenerated. The distance detection section 1031 of the controlcalculation section 103 generates an object information table whichindicates, in association with each object, the position of an object,the size of an object, the S/N ratio of an object, and the requiredspread angle Hh for an object, which are indicated by the respectiveinformation acquired. Then, the distance detection section 1031 storesthe object information table in the storage section, not shown. FIG. 13shows an example of the object information table generated by thedistance detection section 1031. A relative speed in the table shown inFIG. 13 will be described later. The above is the description of theobject identification process by the control calculation section 103.When the control calculation section 103 completes the objectidentification process for one emission region, the control calculationsection 103 performs an individual measurement process for individuallymeasuring objects existing in the same emission region identified in theobject identification process. In the following, as an example of theindividual measurement process, a case will be described in which, afterthe object identification process for the emission region Hr1 iscompleted, the individual measurement process for individually measuringthe objects existing in the identified emission region Hr1 is performed.

For performing the individual measurement process for the emissionregion Hr1, the control calculation section 103 firstly causes thedistance detection section 1031 to provide the detection section 102with an instruction to start a charge storage for the first time periodas described above. Thereby, the control calculation section 103 causesthe detection section 102 to start the charge storage. Then, when thefirst time period elapses after the instruction to start a chargestorage for the first time period has been provided, the controlcalculation section 103 causes the distance detection section 1031 toindicate, to the emission section 101, the position of and the requiredspread angle Hh for one object (hereinafter referred to as an individualobject) which is indicated in the object information table. The emissionsection 101, to which the position of the individual object and therequired spread angle Hh for the individual object have been indicated,drives the driving section, not shown, so as to emit, for theaforementioned emission period, the laser light Lk toward the positionof the individual object which has been indicated, at the requiredspread angle Hh which has been indicated. At this time, the controlcalculation section 103 causes the detection section 102 to start acharge storage for the second time period. Thus, a charge correspondingto the amount of the reflected light, received by the light-receivingelement, of the laser light Lk emitted toward the individual objectwhich is indicated by the distance detection section 1031 is stored foreach light-receiving element.

When the third time period elapses after the control calculation section103 has caused the distance detection section 1031 to provide thedetection section 102 with the instruction to start receiving the light,the distance detection section 1031 of the control calculation section103 detects a charge in each light-receiving element of the detectionsection 102, and then the control calculation section 103 calculates arelative distance St as described above. At this time, the charge ineach light-receiving element, which is detected by the distancedetection section 1031, is a charge stored as a result of reception ofthe reflected light of the laser light Lk which has a higher lightenergy density, that is, the reflected light which has higher intensity,because the laser light Lk has been emitted toward the individual objectat the required spread angle Hh which is smaller than the emissionregion angle Hrk1 as described above. Therefore, an accuracy of therelative distance St calculated at this time by the distance detectionsection 1031 is higher than an accuracy of the relative distance Stcalculated at the time when the laser light Lk is emitted to the entireemission region FM.

When the laser light Lk is emitted toward the individual object and therelative distance St is calculated, the distance detection section 1031of the control calculation section 103 generates relative distanceinformation Sj which indicates each calculated relative distance St anda light-receiving element in association with each other, as describedabove. The relative distance information Sj generated at this time isrelative distance information Sj generated based on the reflected lightof the laser light Lk emitted toward the individual object which isindicated by the object information table. When the relative distanceinformation Sj is generated, the distance detection section 1031 of thecontrol calculation section 103 generates distance image information Kjindicating a distance image obtained when the laser light Lk is emittedtoward the individual object.

When the distance detection section 1031 of the control calculationsection 103 generates the relative distance information Sj, the positioncalculation section 1032 of the control calculation section 103 acquiresthe generated relative distance information Sj. When the positioncalculation section 1032 of the control calculation section 103 acquiresthe relative distance information Sj, the position calculation section1032 of the control calculation section 103 generates reflection pointinformation Hj, as in the object identification process.

When the position calculation section 1032 of the control calculationsection 103 generates the reflection point information Hj, the obstacleidentification section 1033 of the control calculation section 103acquires the generated reflection point information Hj. Moreover, whenthe distance detection section 1031 of the control calculation section103 generates the distance image information Kj, the obstacleidentification section 1033 of the control calculation section 103acquires the generated distance image information Kj. When the obstacleidentification section 1033 acquires the reflection point information Hjand the distance image information Kj, the control calculation section103 generates object position information Tj and size information Oj, asin the object identification process. The position of the individualobject, which is indicated by the object position information Tjgenerated at this time, is a highly accurate position which iscalculated based on the relative distance St having the high accuracy.

When the obstacle identification section 1033 of the control calculationsection 103 generates the object position information Tj, the distancedetection section 1031 of the control calculation section 103 acquiresthe generated object position information Tj. When the distancedetection section 1031 acquires the object position information Tj, thecontrol calculation section 103 updates the position of the individualobject, which is indicated by the object information table and has beenindicated to the emission section 101, into a position having anincreased accuracy, which is indicated by the acquired object positioninformation Tj. When the positions of all the individual objectsindicated by the object information table are updated in theabove-described manner, the control calculation section 103 completesthe individual measurement process for the emission region Hr1. Theabove is the description of the individual measurement process forindividually measuring objects existing in the same emission regionidentified in the object identification process.

In performing the individual measurement process, the controlcalculation section 103 may update the positions of the individualobjects indicated by the object information table, sequentially from theposition of the closest individual object.

When the object identification process and the individual measurementprocess for one emission region are completed, the control calculationsection 103 determines whether or not the emission region having thenext greatest emission distance after the emission distance of theemission region having been measured is in advance stored in a storagesection, not shown. For example, the control calculation section 103determines whether or not the emission region Hr2 having the nextgreatest emission distance after the emission distance of the emissionregion Hr1, which are shown as an example in FIG. 9, is in advancestored in the storage section, not shown. When the control calculationsection 103 determines that the emission region having the next greatestemission distance is stored, the control calculation section 103performs the object identification process and the individualmeasurement process for that emission region. By performing the objectidentification process and the individual measurement process for eachemission region, the control calculation section 103 generates theobject information table for each emission region, and updates thepositions of the individual objects, which are indicated by thegenerated object information table, into positions having an increasedaccuracy. On the other hand, when the control calculation section 103determines that the emission region having the next greatest emissiondistance is not stored in the storage section which is not shown, forexample, when the measurement for the emission region Hr3 shown as anexample in FIG. 9 is completed, the control calculation section 103re-performs the object identification process and the individualmeasurement process for the emission region having the smallest emissiondistance, such as the emission region Hr1.

However, in a case where the control calculation section 103 cannotidentify an object reflection point Th in performing the objectidentification process for one emission region, that is, in a case whereno object exists in the emission region, the control calculation section103 stops the object identification process, and then, withoutperforming the individual measurement process, determines whether or notthe emission region having the next greatest emission distance is inadvance stored in the storage section, not shown, as described above.

When the control calculation section 103 re-performs the objectidentification process for the emission region for which the objectinformation table has been already generated, the control calculationsection 103 updates object information which is indicated by thealready-generated object information table into information which isgenerated as result of the re-performed object identification process.In a case where, as a result of re-performing the object identificationprocess for the emission region for which the object information tablehas been already generated, the control calculation section 103identifies an object which is not indicated by the already-generatedobject information table, the control calculation section 103 addsinformation of that object to the already-generated object informationtable.

Hereinafter, a description will be given of a relative speed which isindicated by the object information table generated by the distancedetection section 1031 of the control calculation section 103. Thecontrol calculation section 103 performs the object identificationprocess and the individual measurement process for the emission regionfor which the object information table has been already generated, andthereby calculates a relative speed between the object measuring deviceand the object existing in the emission region. In more detail, for eachindividual object indicated by the object information table, the controlcalculation section 103: calculates, as the relative speed, a differenceper unit time between the position of the object, which is calculated inthe most recent individual measurement process for an emission region,and the position of the object, which has been calculated in theimmediately preceding individual measurement process for the sameemission region; and stores the relative speed as information indicatedby the object information table such that the relative speed isassociated with each individual object.

The above is the detailed description of the operations of the objectmeasuring device 1 according to the present embodiment. In the abovedescription of the object identification process, the controlcalculation section 103 stores the positions of the objects, which areindicated by the object position information Tj generated by theobstacle identification section 1033, as the positions to be indicatedin the object information table, and then the control calculationsection 103 updates the stored positions of the objects into thepositions measured in the individual measurement process, respectively.However, the control calculation section 103 may directly store thepositions of the objects measured in the individual measurement process,as information to be indicated in the object information table, withoutstoring the positions indicated by the object position information Tj,as information to be indicated in the object information table.

Next, with reference to a flow chart shown in FIG. 14, a descriptionwill be given of a process performed when the control calculationsection 103 of the present embodiment operates the distance detectionsection 1031, the position calculation section 1032, the obstacleidentification section 1033, and the spread angle determination section1034, in the above-described manner, to measure an object. The processshown in a flow chart of FIG. 14 is started at a predetermined time,such as at the time when an ignition key of an own vehicle having theobject measuring device 1 mounted thereon is turned on, at the time whenan own vehicle having the object measuring device 1 mounted thereon soas to measure an area behind the own vehicle as shown in FIG. 1 isshifted into a reverse gear position, and the like.

In step S101, the control calculation section 103 performs the objectidentification process for a selected emission region among a pluralityof predetermined emission regions. When the control calculation section103 performs the processing of step S101 for the first time, that is,when no emission region has been selected, the control calculationsection 103 performs the object identification process on the assumptionthat the emission region having the smallest emission distance has beenselected. When the processing of step S101 is completed, the controlcalculation section 103 advances the processing to step S102.

In step S102, the control calculation section 103 determines whether ornot the obstacle identification section 1033 can identify an objectreflection point Th during the object identification process for theemission region selected in step S101. When, in step S102, the controlcalculation section 103 determines that an object reflection point Thcan be identified, the control calculation section 103 advances theprocessing to step S103. On the other hand, when, in step S102, thecontrol calculation section 103 determines that an object reflectionpoint Th cannot be identified, the control calculation section 103advances the processing to step S105.

In step S103, the control calculation section 103 generates an objectinformation table as a result of continuously performing the objectidentification process for the emission region by the processing of stepS101. When the processing of step S103 is completed, the controlcalculation section 103 advances the processing to step S104.

In step S104, the control calculation section 103 performs theindividual measurement process for an object indicated by the objectinformation table which has been generated in step S103. When theprocessing of step S104 is completed, the control calculation section103 advances the processing to step S105.

In step S105, the control calculation section 103 determines whether ornot the emission region having the next greatest emission distance isstored in the storage section, not shown. When, in step S105, thecontrol calculation section 103 determines that the emission regionhaving the next greatest emission distance is stored, the controlcalculation section 103 advances the processing to step S106. On theother hand, when the control calculation section 103 determines that theemission region having the next greatest emission distance is notstored, the control calculation section 103 advances the processing tostep S107.

In step S106, the control calculation section 103 selects the emissionregion having the next greatest emission distance, among emissionregions stored in the storage section, not shown. When the processing ofstep S106 is completed, the control calculation section 103 returns theprocessing to step S101.

In step S107, the control calculation section 103 selects the emissionregion having the smallest emission distance, among emission regionsstored in the storage section, not shown. When the processing of stepS107 is completed, the control calculation section 103 returns theprocessing to step S101.

The above is the description of the processing performed by the controlcalculation section 103 according to the present embodiment. The objectmeasuring device 1 according to the present embodiment performs theindividual measurement process by emitting, at a smaller spread angleHk, the laser light Lk to an object existing in the emission region forwhich the object identification process has been performed. Therefore,information of objects existing in the same emission region can beindividually measured with a high accuracy.

The object measuring device 1 according to the present embodimentperforms the object identification process by emitting the laser lightLk at one emission region angle Hrk, and performs the individualmeasurement process. Then, the object measuring device 1 performs theobject identification process for the emission region having the nextgreatest emission distance, by emitting the laser light Lk at a smalleremission region angle Hrk, and performs the individual measurementprocess for the emission region having the next greatest emissiondistance. Consequently, in the object measuring device 1 according tothe present embodiment, an object that cannot have been identifiedmerely by emitting the laser light Lk at one emission region angle Hrkcan be identified by emitting, at a smaller emission region angle Hrk,the laser light Lk having a high light energy density as describedabove.

In addition, in the above description of the first embodiment, anemission period in the object identification process and an emissionperiod in the individual measurement process are set to the same timeperiod. As a result, an emission period in the object identificationprocess for measuring the entire emission region and an emission periodin the individual measurement process for measuring each individualobject are the same, which enables an emission period for individuallymeasuring one object to be relatively prolonged within a predeterminedmeasurement period. The fact that the emission period can be prolongedmeans that the time period (second time period) for the charge storagein the detection section 102 can be prolonged. This can improve the S/Nratio to thereby provide a measurement with an increased accuracy. Here,the predetermined measurement period is a time period required forcompleting the object identification process and the individualmeasurement process for one emission region. The emission period in theobject identification process and the emission period in the individualmeasurement process may be set as different emission periods, as long asthe accuracy in the individual measurement process can be increased.

Moreover, as described above, by narrowing the spread angle Hk, the S/Nratio can be improved to thereby provide a measurement with an increasedaccuracy. However, if the entire emission region is scanned with thelaser light Lk having a narrow spread angle Hk, a time necessary forscanning the entire emission region increases. In the object measuringdevice 1 according to the first embodiment, in the object identificationprocess, the entire emission region is measured to identify objects, andthen, in the individual measurement process, an object that has to bemeasured is measured by being irradiated with the laser light Lk havinga smaller spread angle Hk. As a result, an accurate measurement can beperformed in a short time.

Furthermore, in the object measuring device 1 according to the firstembodiment, the object identification process is performed and objectsare recognized by identifying, among reflection points of vehicles,pedestrians, and obstacles including the road surface, reflection pointsother than the road surface. Then, only the recognized objects aremeasured in the individual measurement process. Consequently, anaccurate measurement can be performed, without an unnecessarymeasurement of an object that does not have to be measured.

Second Embodiment

An object measuring device 1 according to a second embodiment corrects adirection in which a laser light Lk is emitted and a spread angle Hk ofthe laser light Lk, based on a distance image indicated by the distanceimage information Kj. In the following, a description will be given ofan operation, in correction, of the object measuring device 1 accordingto the present embodiment. The control calculation section 103 accordingto the second embodiment is different from the control calculationsection 103 according to the first embodiment, in that the controlcalculation section 103 according to the second embodiment functionsalso as a correction section 1035. Accordingly, a configuration of theobject measuring device 1 according to the second embodiment, andfunctions, except the function as the correction section 1035, of thecontrol calculation section 103 according to the second embodiment, arethe same as those of the control calculation section 103 according tothe first embodiment, and therefore a description thereof will beomitted.

FIG. 15 is a diagram showing an example of a pattern image Pt which isused for correcting an emission direction and a spread angle Hk of thelaser light Lk emitted by the object measuring device 1 according to thesecond embodiment. The control calculation section 103 stores, in astorage section which is not shown, a pattern image Pt corresponding toa reference emission region Khr for a correction. The pattern image Ptis an image previously formed so as to indicate an irradiation region,on a distance image, of a laser light Lk which is emitted from theemission section 101 to the reference emission region Khr, which isdefined by a predetermined reference direction Kh and a predeterminedreference spread angle Khk, when the own vehicle is substantiallyparallel to a flat road surface (for example, when the bottom surface ofthe own vehicle is substantially parallel to the flat road surface). Thepattern image Pt shown as an example in FIG. 15 is an image previouslyformed so as to indicate an irradiation region obtained when a laserlight Lk is emitted to the flat road surface from the object measuringdevice 1, which is mounted in the manner described above in the firstembodiment with reference to FIG. 1. Therefore, the pattern image Ptshown in FIG. 15 has a distorted circle shape.

When a correction process is started, firstly, the control calculationsection 103 causes the distance detection section 1031 to provide thedetection section 102 with an instruction to start a charge storage forthe first time period. When the first time period elapses after theinstruction to start a charge storage for the first time period has beenprovided, the control calculation section 103 causes the distancedetection section 1031 to instruct the emission section 101 to emit thelaser light Lk at the reference spread angle Khk in the referencedirection Kh. When the third time period elapses after the controlcalculation section 103 has provided the instruction to start a chargestorage for the first time period, the control calculation section 103detects a charge stored in each light-receiving element of the detectionsection 102 as described in the first embodiment, and causes thedistance detection section 1031 to generate distance image informationKj indicating the aforementioned distance image.

When the distance image information Kj is generated, the correctionsection 1035 of the control calculation section 103 acquires thegenerated distance image information Kj. When the correction section1035 acquires the distance image information Kj, the correction section1035 of the control calculation section 103 identifies an irradiationregion of the laser light Lk, on the distance image indicated by theacquired distance image information Kj. Any known method may be adoptedas a method for identifying, by the correction section 1035 of thecontrol calculation section 103, an irradiation region of the laserlight Lk on the distance image. As an example, a pattern matching methodusing a predetermined image may be adopted. In such a case, an image tobe used may be the pattern image Pt.

When the correction section 1035 acquires the distance image informationKj, the control calculation section 103 compares the irradiation regionof the laser light Lk on the distance image indicated by the acquireddistance image information Kj, with the irradiation region on thepattern image Pt prestored in the storage section which is not shown.

To be more specific, the correction section 1035 of the controlcalculation section 103 calculates the center of an irradiation regionon a distance image Kg which is indicated by the distance imageinformation Kj, as shown in FIG. 16A. When the center of the irradiationregion on the distance image Kg is calculated, the control calculationsection 103 superimposes the distance image Kg and the pattern image Pton each other, and the correction section 1035 detects the amount ofdeviation of the center of the irradiation region on the distance imageKg from the center of the irradiation region on the pattern image Pt, asshown in FIG. 16B. When the correction section 1035 detects the amountof deviation of the center of the irradiation region, the controlcalculation section 103 causes the correction section 1035 to providethe emission section 101 with an instruction to set, as the referencedirection Kh, an angle resulting from changing the angle of the opticalaxis of the laser light Lk in accordance with the detected amount ofdeviation.

When the reference direction Kh is corrected, the correction section1035 of the control calculation section 103 corrects the referencespread angle Khk. FIG. 16C is a diagram showing the irradiation regionon the distance image and the irradiation region on the pattern image Ptwith the centers of the respective irradiation regions being coincidentwith each other. When the reference spread angle Khk is deviated, adeviation occurs between the irradiation region of the laser light Lkemitted from the emission section 101 and the irradiation region on thepattern image Pt, even though the centers of the respective irradiationregions coincide with each other, as shown in FIG. 16C. The correctionsection 1035 of the control calculation section 103 detects a deviationwhich occurs when the center of the irradiation region of the laserlight Lk and the center of the irradiation region on the pattern imagePt coincide with each other. When the correction section 1035 detectsthe amount of deviation of the irradiation region of the laser light Lk,the control calculation section 103 causes the correction section 1035to provide the emission section 101 with an instruction to set, as thereference spread angle Khk, a spread angle Hk resulting from changingthe spread angle Hk of the laser light Lk in accordance with thedetected amount of deviation.

When provided with the instructions indicating the reference directionKh and the reference spread angle Khk, the emission section 101 sets thereference direction Kh and the reference spread angle Khk which areindicated by the instructions, as a reference of the direction of theoptical axis of the laser light Lk and a reference of the spread angleKhk, respectively. Thus, the emission section 101 emits the laser lightLk in accordance with an instruction provided thereafter.

The above is the description of the correction process performed by thecontrol calculation section 103 according to the second embodiment.Next, conditions under which the control calculation section 103according to the second embodiment starts the correction process will bedescribed. The control calculation section 103 starts the correctionprocess, when at least one of the three conditions described below issatisfied.

The first condition is that, based on a change in brightness in thedistance image, it can be determined that the own vehicle issubstantially parallel to the road surface. More specifically, each timethe distance detection section 1031 generates distance image informationKj, the control calculation section 103 causes the correction section1035 to acquire the distance image information Kj and to determinewhether or not the amount of change, over a predetermined time period,in the brightness values of a plurality of predetermined pixels in thedistance image, which is generated as described in the first embodiment,is equal to or lower than a predetermined threshold. When the correctionsection 1035 determines that the amount of change, over thepredetermined time period, in the brightness values of the plurality ofpredetermined pixels in the distance image is equal to or lower than thepredetermined threshold, the control calculation section 103 candetermine that the own vehicle is substantially parallel to the roadsurface. As described above, the pattern image Pt is an image previouslyformed so as to indicate an irradiation region, on a distance image, ofa laser light Lk which is emitted from the emission section 101 to thereference emission region Khr, which is defined by the predeterminedreference direction Kh and the predetermined reference spread angle Khk,when the own vehicle is substantially parallel to a flat road surface.Accordingly, the control calculation section 103 can perform acorrection with an increased accuracy, by causing the correction section1035 to compare the distance image, which is indicated by the distanceimage information Kj generated when the own vehicle is substantiallyparallel to the road surface, with the pattern image Pt.

The second condition is that, the control calculation section 103 causesthe correction section 1035 to obtain the variance G among thebrightness of respective pixels included in each divided region, whichis obtained as a result of dividing the distance image into a pluralityof divided regions, and the control calculation section 103 candetermine that the obtained variance a is equal to or lower than apredetermined threshold. For example, when the distance image includes apixel that has a brightness value corresponding to a puddle, brightnessvalues over the entire distance image becomes largely uneven, whichincreases the possibility that the correction section 1035 cannotidentify an accurate irradiation region of the laser light Lk on thedistance image. Therefore, the control calculation section 103 cansurely perform an accurate correction, by starting the correctionprocess when the correction section 1035 determines that the variance σamong the brightnesses of the respective pixels included in each dividedregion is equal to or lower than the predetermined threshold.

The third condition is that the correction section 1035 of the controlcalculation section 103 can determine that a change in orientation ofthe own vehicle is small, by using an acceleration sensor, a yaw ratesensor, a vehicle speed sensor, and the like, which are provided in theown vehicle. More specifically, the control calculation section 103causes the correction section 1035 to determine whether or not anacceleration, a yaw angle, and a speed, of the own vehicle, which thecorrection section 1035 have detected by using the acceleration sensor,the yaw rate sensor, and the vehicle speed sensor, respectively,provided in the own vehicle, are equal to or lower than predeterminedthresholds, respectively. When the acceleration, a yaw angle, and aspeed, of the own vehicle are equal to or lower than the predeterminedthresholds, respectively, it can be considered that a change inorientation of the own vehicle is small, and therefore the own vehicleis substantially parallel to the road surface. Thus, because of the samereason as described in relation to the first condition above, thecorrection section 1035 of the control calculation section 103 canperform a correction with an increased accuracy.

The above is the description of the object measuring device 1 accordingto the second embodiment. In the object measuring device 1 according tothe second embodiment, a correction can be automatically performed whenat least one of the above-described conditions is satisfied duringoperation, and thus the laser light Lk can be always emitted from theemission section 101 at an accurate spread angle in an accuratedirection.

In all the above embodiments, a case in which the object measuringdevice 1 is mounted in the vehicle has been described as an example.However, the object measuring device according to the present inventionmay be mounted in any object, as long as the object exists on the roadsurface or a face equivalent to the reference plane Km mentioned above.

Moreover, in all the embodiments described above, a laser light isadopted as a light source of the emission section 101. However, inanother embodiment, an LED (Light Emitting Diode) may be adopted as thelight source.

In still another embodiment, the diffusion plate 1014 may be removedfrom the emission section 101 and the emission section 101 may beconfigured to emit a laser light Lk to a region according to aninstruction, as shown in FIG. 17.

In further still another embodiment, the emission section 101 in whichthe second reflecting plate 1012 is fixed may be configured to emit alaser light Lk to a region according to an instruction, as shown in FIG.18.

In further still another embodiment, as an electromagnetic wave, a radiowave may be emitted instead of the laser light Lk. In such a case, theemission section described in the first embodiment may be configured ofa radio wave emission section which emits a radio wave, first and secondreflecting plates which respectively reflect the radio wave in themanner described in the first embodiment, a diffusion plate whichdiffuses the radio wave in the manner described in the first embodiment,and a lens which emits the radio wave in the manner described in thefirst embodiment, instead of the light source 1011, the first and secondreflecting plates 1012 and 1013, the diffusion plate 1014, and the lens1015, respectively. In addition, instead of the light-receiving elementsarranged in a grid pattern on the flat substrate, a receiving element,which is capable of receiving a reflected wave of the radio wave emittedfrom the emission section, may receive the reflected wave to perform theprocess described in the first embodiment.

The control calculation section 103 may be realized by, instead of theCPU, an LSI, a microcomputer, or the like, interpreting and executingpredetermined program data which enables execution of theabove-described process and is stored in a storage device (a ROM, a RAM,a hard disk, or the like). Moreover, the above-described CPU may be aCPU that forms an ECU (Electric Control Unit) mounted in a mobile bodysuch as an automobile. In such a case, the program data may beintroduced into the storage device via a storage medium, or may beexecuted directly on the storage medium. Here, the storage medium maybe: a semiconductor memory such as a ROM, a RAM, and a flash memory; amagnetic disk memory such as a flexible disk and a hard disk; an opticaldisk memory such as a CD-ROM, a DVD, and a BD; a memory card; and thelike.

Needless to say, any combination of the above-described embodiments isacceptable.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention enables an object existing in a measurement rangeto be measured with an increased accuracy, and is applicable to anobject measuring device mounted in a mobile body such as a vehicle, forexample.

1. An object measuring device mounted in a vehicle, comprising: a firstemission section that emits, at a predetermined first spread angle, anelectromagnetic wave to a predetermined region; a reception section thatreceives, by receiving elements arranged in a grid pattern, a reflectedwave of the electromagnetic wave; a distance detection section thatdetects, for each of the receiving elements, a relative distance betweeneach receiving element and a reflection point of the reflected wave,based on a reception time period from emission of the electromagneticwave to reception of the reflected wave; a calculation section thatcalculates position information which indicates a position of thereflection point by using as a reference a position of mounting in thevehicle, based on at least the relative distance and an angle at whichthe reception section is mounted in the vehicle; a reference planecalculation section that calculates, as a reference plane, a planeparallel to a bottom surface of the vehicle, based on an orientation ofthe vehicle; an identification section that identifies, based on theposition information, adjacent reflection points, wherein a differencein height from the reference plane between the adjacent reflectionpoints is equal to or larger than a predetermined first threshold; and asecond emission section that emits, at a second spread angle which issmaller than the first spread angle, the electromagnetic wave to thereflection points, when the identification section identifies thereflection points.
 2. The object measuring device according to claim 1,wherein, when the identification section identifies the reflectionpoints, the second emission section emits the electromagnetic wave tothe reflection points, in order starting from the reflection pointhaving the smallest relative distance.
 3. The object measuring deviceaccording to claim 1, further comprising an object identificationsection that: groups the reflection points identified by theidentification section such that the adjacent reflection points whichare spaced from each other over a distance equal to or less than apredetermined second threshold are in one group; and identifies thereflection points in one group, as one object, wherein the secondemission section emits the electromagnetic wave to the reflection pointsof the object identified by the object identification section.
 4. Theobject measuring device according to claim 3, wherein: the secondemission section emits the electromagnetic wave to the reflectionpoints, in order from the reflection point of the object closest to theobject measuring device, among objects identified by the objectidentification section; and the distance detection section detects therelative distance for each object, in the order in which the secondemission section has emitted the electromagnetic wave to the objects. 5.The object measuring device according to claim 4, wherein the distancedetection section detects the relative distance for each object, basedon the reception time period for receiving the reflected wave having thehighest intensity, among reflected waves reflected from the reflectionpoints which have been grouped as the one object.
 6. The objectmeasuring device according to claim 5, wherein, after the distancedetection section detects all the relative distances for the respectiveobjects, the first emission section emits, at a third spread angle whichis smaller than the first spread angle, the electromagnetic wave to anext predetermined region immediately following the predeterminedregion.
 7. The object measuring device according to any one of claims 4to 6, further comprising a speed detection section that detects, foreach object, a relative speed between the object measuring device andthe object, based on the most recent relative distance and thepreviously detected relative distance which are respectively detected bythe distance detection section.
 8. An object measuring method which isperformed in an object measuring device mounted in a vehicle, the objectmeasuring method comprising: a first emission step of emitting, at apredetermined first spread angle, an electromagnetic wave to apredetermined region; a reception step of receiving, by receivingelements arranged in a grid pattern, a reflected wave of theelectromagnetic wave; a distance detection step of detecting, for eachof the receiving elements, a relative distance between each receivingelement and a reflection point of the reflected wave, based on areception time period from emission of the electromagnetic wave toreception of the reflected wave; a calculation step of calculatingposition information which indicates a position of the reflection pointby using as a reference a position of mounting in the vehicle, based onat least the relative distance and an angle at which the receivingelement is mounted in the vehicle; a reference plane calculation step ofcalculating, as a reference plane, a plane parallel to a bottom surfaceof the vehicle, based on an orientation of the vehicle; anidentification step of identifying, based on the position information,adjacent reflection points, wherein a difference in height from thereference plane between the adjacent reflection points is equal to orlarger than a predetermined first threshold; and a second emission stepof emitting, at a second spread angle which is smaller than the firstspread angle, the electromagnetic wave to the reflection points, whenthe reflection points are identified in the identification step.